Cooking hood with air curtain

Abstract

 A cooking hood has a suction duct configured to suck up a first airflow from a region under the cooking hood. A filter is provided in the suction duct to filter out grease or other material. The cooking hood blows down a second airflow through an air curtain at least partly around said region. The cooking hood condenses moisture from the second airflow before blowing down the second air flow in the air curtain.

Description

[0001] The invention relates to a cooking hood with a condenser for condensing moisture from air sucked up over a cooking range.

[0002] US patent No. 4,450,756 describes a cooking hood that provides for an air curtain around a kitchen range. Cooking hoods serve to remove air with fumes from an area over a cooking range where food is prepared in the kitchen. The cooking hood of US 4,450,756 sucks up air from over the cooking range, blows it through a filter and then guides it down in an air curtain around the periphery of the cooking range. The filter removes fumes from the air before blowing the air back into the kitchen in the air curtain. US 4,450,756 discloses a charcoal filter and an unspecified general filter for this purpose. The air curtain keeps cooking fumes over the range from escaping into the kitchen. As a result the fumes do not present a problem even if a relatively small flow of air up from the kitchen range into the cooking hood is used.

[0003] Alternative cooking hoods are known which take the air from over the cooking range and exhaust this air into the kitchen without using an air curtain. As in the case.of the cooking hood with an air curtain this solution avoids costly ventilation channels. However, the effectiveness of both types of cooking hood depends on the effectiveness of the filter. If the filter does not sufficiently remove fumes, the cooking hood is of little use.

[0004] Among others, it is an object of the invention to provide for an cooking hood that makes it possible to improve removal of fumes.

[0005] According to the invention, the cooking hood is provided with a condenser in the duct to the outlet for blowing down the air curtain. It has been found that the effectiveness of filters in the flow of air up from the cooking range may be adversely affected by the humidity of the airflow. In the case of an active coal filter, for example, the effectiveness reduces when the relative humidity increases above seventy percent. By using dried air in the air curtain, the overall humidity of the airflow up from the cooking range is reduced. Thus the effectiveness of the filter is improved.

[0006] In an embodiment the cooking hood comprises an air humidity sensor coupled to the condenser to control the condenser dependent on the sensed humidity, for example by activating the condenser only if the humidity exceeds a threshold. The sensor may be located at various positions. In one embodiment it is located in the flow of air up into the cooking hood, to measure humidity near the filter. In another embodiment the sensor may be located in the duct to the outlet for the air curtain, before the condenser.

[0007] In an embodiment the inlet for air flow to the duct to the air curtain is separate from an outlet for the air flow from under the cooking hood, in the sense that the outlet for air flow from under the cooking hood blows air into the kitchen and the inlet for air flow to the duct to the air curtain sucks in air from the kitchen. As an alternative a closed circuit could be used, wherein airflow from under the cooking hood flows into the duct to the air curtain. However, separate outlets and inlets have the advantage over the closed circuit alternative that grease that has passed the filters cannot clog the condenser. Also air with a lower temperature from the kitchen is at least mixed in with the air for the air curtain. During cooking on a gas cooker the air above the kitchen range has a high temperature. By using air from the kitchen the efficiency of the dehumidification is higher than if air from over the kitchen range is used.
These and other objects and advantageous aspects will become apparent from a description of an exemplary embodiment using the attached figure.

Figures 1-3 show cooking hoods

[0008] Figure 1 shows a cooking hood comprising a suction duct 10 and an air curtain duct 15. The cooking hood comprises a grease filter 1, a coal filter 6 and a first fan 12 in suction duct 10. Air curtain duct 15 has outlets 16 for forming an air curtain 5 that at least partly surrounds a region from which suction duct sucks up air over the cooking range. The cooking hood comprises a second fan 13 and a condenser 2 in air curtain duct 15. Condenser 2 contains a water drain 3. Suction duct 10 exhausts in an exhaust 18 into the room where the cooking hood is located. Exhaust 18 does not exhaust directly into air curtain duct 15, i.e. it at least allows other air from the kitchen to flow into air curtain duct 15. preferably, the output of exhaust 18 and the input of air curtain duct 15 are directed in mutually opposite directions (as shown) to minimize direct transfer from exhaust 18 to air curtain duct 15. In an embodiment first fan 12, and second fan 13, may be combined, using a first and second set of fan blades, both driven by a single motor via a single axle.

[0009] In operation first fan 12 causes the cooking hood to suck up air from a region over a cooking range. The air is passed through filters 1, 6 and exhausted from the cooking hood through exhaust 18. Second fan 13 sucks in air from outside the cooking hood into the air curtain duct, where the air is fed through condenser 2 to air curtain outlets 16. The outlets 16 are provided substantially all around a perimeter of the cooking range (as seen from above), or at least along an exposed part of the perimeter, e.g. along a front side and a left and right side, if the range is placed against a wall. Air curtain 5 is directed so that it substantially prevents air from over the cooking range to flow out into space adjacent the range, i.e. normally the kitchen.

[0010] Condenser 2 dries the air. In an embodiment condenser 2 at least temporarily reduces the temperature of incoming air, with the effect that moisture in this air condenses. The condensed moisture flows off through water drain 3. As an alternative other drying techniques may be used, such as leading the air past or through a drying agent, but in this case the drying agent may have to be replaced regularly.

[0011] Figure 2 shows an embodiment wherein condenser 2 contains a closed refrigerant circuit 20 with a compressor 22, a refrigerant evaporator 24 and a refrigerant condenser 26. Refrigerant condenser 26 is placed behind refrigerant evaporator 24 in the direction of airflow through air curtain duct 15. In operation, refrigerant evaporates in refrigerant evaporator 24, cooling down air flowing through air curtain duct 15. The cooling causes moisture in the air to condense and flow off through water drain 3. Compressor 22 compresses the evaporated refrigerant and the compressed refrigerant is fed to refrigerant condenser 26 where the refrigerant condenses, giving of heat that is used to warm the air flowing through air curtain duct 15 after moisture has condensed. The refrigeration cycle is completed when the refrigerant flows from the condenser to the evaporator and passes through an expansion organ 21.

[0012] Figure 2 also shows a humidity sensor 28 coupled to compressor 22. Humidity sensor 28 is located in contact with air in air curtain duct before condenser 2. In operation humidity sensor 28 controls activation of compressor 22 when the measured relative humidity of the air is above a threshold and controls deactivation of compressor 22 when the humidity is below the threshold, or a further, lower threshold. In a further embodiment humidity sensor 28 is configured so that the threshold can be set manually. Humidity sensor 28 is used to deactivate condenser 2 when the humidity of the air is so low that it need not be reduced to operate the filters. Alternatively, or in addition, humidity sensor 28 can be used to control cooling strength of condenser 2 dependent on the humidity, increasing the cooling strength with increasing humidity.

[0013] In addition to the humidity sensor, or in an embodiment without the humidity sensor, a temperature sensor may be provided, for sensing the temperature of air flowing to the air curtain. This temperature sensor switches off the condenser when the temperature of the air exceeds a threshold. This may be used to prevent useless operation of the condenser when the air temperature is too high to condense water from the air.

[0014] It should be noted that humidity sensor 28 and closed fluid cooling circuit 20 can be used independent of one another. Closed fluid cooling circuit 20 may be used without humidity sensor 28, for example always when the cooking hood is switched on, or when compressor 22 is manually switched on. Humidity sensor 28 may be located elsewhere, for example in suction duct 10 in front of filters 1,6 or behind. Humidity sensor 28 may also be used in combination with other types of active condenser 2.

[0015] Condenser 2 may be an active condenser, comprising for example a Peltier element to cool the air or some other cooling arrangement.

[0016] Figure 3 shows a cooking hood comprising a suction duct 10 which exhausts in the outlets 16 for generating air curtain 5 and an additional exhaust 18 that does not exhaust into outlets 16. An adjustable vent 4 is provided in series with external exhaust 18. In front of suction duct 10 a grease filter 1 and a coal filter 6 is provided. In suction duct 10 a first fan 12 and a condenser 2 are provided. Condenser 2 contains a water drain 3.

[0017] In operation first fan 12 causes the cooking hood to suck up air from a region over a cooking range. The air is passed through condenser 2 and from there to outlets 16 for the air curtain 5 and the external exhaust 18.

[0018] The capacity of first fan 12 is set so that sufficient air is blown down in air curtain 5 substantially to prevent air from escaping sideways from the cooking range, but not much higher. This has the effect that the rise in temperature and absolute humidity of the air above the cooking range due to heating from the cooking range is maximized. Thus, the capacity for taking up moisture is increased.

[0019] Condenser 2 reduces the temperature of the air that has been sucked up, with the effect to moisture in this air condenses. The condensed moisture flows off through water drain 3. Due to the increased absolute humidity rise the amount of condensed water is higher than for cooler air.

[0020] Comparing the cooking hoods of figures 1 and 3, it may be noted that considerably more condensation power is needed in the cooking hood of figure 3, because the air sucked up from over the cooking range generally has higher temperature and absolute humidity than air from the surroundings. Therefore the cooking hood of figure 1 is advantageous because it works well with a less powerful condenser. On the other hand the cooking hood of figure 1 helps to reduce humidity in the kitchen.

[0021] Adjustable vent 4 is set to release a fraction of the air that has been sucked up outside the air curtain. Thus, the suction capacity is made higher than the supply of air through the air curtain. This has been found to improve the stability of the air curtain and cooking conditions. In the embodiment of the figure the size of this fraction can be adjusted dependent on the fan speed or the amount of heat generated by the cooking range. For example, when more heat is generated the fraction may be set higher and when less heat is generated the fraction may be set lower, or the fraction may even be made zero..

[0022] In another embodiment a fixed vent may be used instead of adjustable vent 4, or an adjustable vent 4 that is set to a fixed position once upon installation of the cooking hood. This provides for less control over temperature and humidity. In another embodiment a control loop may be provided to adjust adjustable vent 4, comprising an air humidity and temperature sensor for sensing humidity and temperature of the air over the cooking range, e.g. in duct 10, and coupled to a control organ of adjustable vent 4 so that the adjustable vent 4 is adjusted to increase the fraction with rising measured temperature.

[0023] A passive condenser may be used, comprising a heat exchanger to cool the air. In an embodiment a counterflow heat exchanger is used, comprising a further duct in parallel with duct 10, but separated from duct 10 by a heat exchange surface. The heat exchanger comprises a further fan, for blowing ambient air through the further duct in a flow direction opposite to the flow direction of duct 10. A counterflow heat exchanger at most has the capacity to cool air to ambient temperature. Under some circumstances this may suffice to remove moisture under typical cooking conditions, provided that the air curtain is used to trap the air for some time before it is fed to the condenser.

[0024] The air curtain serves to trap air above the cooking range, with the effect that the temperature and humidity in the trapped air rises higher than in the case that no air curtain is used. When the trapped air is fed to the condenser a small cooling capacity suffices to reach the condensation point.

Claims

1. A cooking hood, comprising a suction duct configured to suck up a first airflow from a region under the cooking hood with a filter in the suction duct, an air curtain duct coupled to an air curtain outlet directed for blowing down a second airflow through an air curtain at least partly around said region, characterized in that the cooking hood comprises a condenser in the air curtain duct, for condensing moisture from the second airflow before blowing down the second air flow in the air curtain.

2. A cooking hood according to claim 1, wherein the suction duct has an outlet and the air curtain duct has an inlet configured to let in air at least partly from outside the cooking hood, separate from the outlet of the suction duct.

3. A cooking hood according any one of the preceding claims, comprising a humidity sensor coupled to the condenser, for controlling operation of the condenser.

4. A cooking hood according to claim 3, wherein the humidity sensor is located in the air curtain duct, preceding the condenser in a direction of air flow to the air curtain outlet.

5. A cooking hood according any one of the preceding claims wherein the condenser comprises a closed refrigerant circuit with a refrigerant condenser and a refrigerant evaporator located in the air curtain duct, the refrigerant evaporator being located in front of the refrigerant condenser in a direction of air flow to the air curtain outlet.

6. A cooking hood according to claim 1, arranged to exhaust at least part of the first airflow directly into the air curtain duct.

7. A cooking hood according to Claim 6, comprising a vent for discharging a fraction of the air from the condenser outside the air curtain.

8. A cooking hood according to Claim 7, wherein the vent is an adjustable vent, which allows the fraction to be adjusted.

9. A cooking hood according any one of the preceding claims, comprising a temperature sensor coupled to the condenser, for controlling operation of the condenser.

10. A method of controlling spreading of fumes from a cooking range, the method comprising

- sucking up air from a region over the cooking range;

- filtering the sucked up air

- blowing an air curtain at least partly around said region,

characterized by

- condensing moisture from an airflow for use in the air curtain, before forming the air curtain from said airflow.

Drawing